Advanced Physics for Brachytherapy 2018

The problem …

For brachytherapy photons: • secondary e- ranges are small relative to photon m.f.p. • e- radiative energy loss is negligible • CPE can be assumed to exist at all points (except close to a source or high Z materials)

1

Energy [keV]

CSDA-range electrons [g/cm 2 ]



[cm]

30

1.8E-03 1.2E-02 1.1E-01 4.4E-01

2.5 5.6 8.9

100 350

1000

14

Dose to a point can be approximated by collision KERMA throughout a geometry of mm sized voxel elements

In short, to know the dose distribution one needs to know the energy distribution of fluence, Φ Ε , at all points of a geometry:

Table from: Venselaar, Baltas, Meigooni, Hoskin (Eds), Comprehensive Brachytehrapy: physical and clinical aspects. CRC Press, Taylor & Francis, © 2013